The present invention relates to a nucleic acid constructs, pharmaceutical compositions and methods which can be used to downregulate angiogenesis in specific tissue regions of a subject. More particularly, the present invention relates to nucleic acid constructs, which can be used to activate apoptosis in specific cell subsets, thus, enabling treatment of diseases characterized by excessive or aberrant neovascularization or cell growth.
Angiogenesis is the growth of new blood vessels, a process that depends mainly on locomotion, proliferation, and tube formation by capillary endothelial cells. During angiogenesis, endothelial cells emerge from their quiescent state and proliferate rapidly. Although the molecular mechanisms responsible for transition of a cell to angiogenic phenotype are not known, the sequence of events leading to the formation of new vessels has been well documented [Hanahan, D., Science 277, 48-50, (1997)]. The vascular growth entails either endothelial sprouting [Risau, W., Nature 386, 671-674, (1997)] or intussusceptions [Patan, S., et al; Microvasc. Res. 51, 260-272, (1996)]. In the first pathway, the following sequence of events may occur: (a) dissolution of the basement of the vessel, usually a post capillary venule, and the interstitial matrix; (b) migration of endothelial cells toward the stimulus; (c) proliferation of endothelial cells trailing behind the leading endothelial cell (s); (d) formation of lumen (canalization) in the endothelial array/sprout; (e) formation of branches and loops by confluencial anastomoses of sprouts to permit blood flow; (f) investment of the vessel with pericytes (i.e., periendothelial cells and smooth muscle cells); and (g) formation of basement membrane around the immature vessel. New vessels can also be formed via the second pathway: insertion of interstitial tissue columns into the lumen of preexisting vessels. The subsequent growth of these columns and their stabilization result in partitioning of the vessel lumen and remodeling of the local vascular network.
A variety of angiogenic factors govern the angiogenic process. It is understood that during pathology, the fine balance between pro-angiogenic factors and anti-angiogenic factors is disrupted, thereby eliciting nonself-limiting endothelial and periendothelial cell-proliferation. Until recently, the angiogenesis that occurs in diseases of ocular neovascularization, arthritis, skin diseases, and tumors, had been difficult to suppress therapeutically.
Therefore, the fundamental goal of all anti-angiogenic therapy is to return foci of proliferating microvessels to their normal resting state, and to prevent their regrowth [Cancer: Principles & Practice of Oncology, Fifth Edition, edited by Vincent T. DeVita, Jr., Samuel Hellman, Steven A. Rosenberg. Lippincott-Raven Publishers, Philadelphia. (1997)].
Anti-angiogenic therapy is a robust clinical approach, as it can delay the progression of tumor growth (e.g., retinopathies, benign and malignant angiogenic tumors).
In general, every disease caused by uncontrolled growth of capillary blood vessels such as diabetic retinopathy, psoriasis, arthritis, hemangiomas, tumor growth and metastasis is a target for anti-angiogenic therapy.
For example, the progressive growth of solid tumors beyond clinically occult sizes (e.g., a few mm3) requires the continuous formation of new blood vessels, a process known as tumor angiogenesis. Tumor growth and metastasis are angiogenesis-dependent. A tumor must continuously stimulate the growth of new capillary blood vessels to deliver nutrients and oxygen for the tumor itself to grow. Therefore, either prevention of tumor angiogenesis or selective destruction of tumor's existing blood vessels (vascular targeting therapy) underlies anti-angiogenic tumor therapy.
Recently, a plethora of anti-angiogenic agents has been developed for the treatment of malignant diseases, some of which are already under clinical trials (for review see Herbst et al. (2002) Semin. Oncol. 29:66-77).
The most studied target for tumor anti-angiogenic treatment is the dominant process regulating angiogenesis in human i.e., the interaction of vascular endothelial growth factor (VEGF) with its receptor (VEGFR). Agents which regulate VEGFR pro-angiogenic action include (i) antibodies directed at the VEGF protein itself or to the receptor (e.g., rhuMAb VEGF); (ii) small molecule compounds directed to the VEGFR tyrosine kinase (e.g., ZD6474 and SU5416); (iii) VEGFR targeted ribozymes.
Other novel angiogenesis inhibitors include 2-Methoxyestradiol (2-ME2) a natural metabolite of estradiol that possesses unique anti-tumor and anti-angiogenic properties and angiostatin and endostatin-proteolytic cleavage fragments of plasminogen and collagen XVIII, respectively.
Though promising in pre-clinical models, to date systemic administration of all anti-angiogenic agents tested in clinical trials, have shown limited rate of success and considerable toxicities including thrombocytopenia, leukopenia and hemoptysis. These results suggest that there may be limits to the use of current tumor anti-angiogenic agents as therapy for advanced malignancies. O'Reilly et al. have shown that the latency between the initiation of anti-angiogenic therapy and antitumor effect may result in initial tumor progression before response to therapy [O'Reilly S et al. (1998) Proc Am Soc Clin Oncol 17:217a]. Furthermore, recent studies suggest that the regulation of angiogenesis may differ among capillary beds, suggesting that anti-angiogenic therapy may need to be optimized on an organ/tissue-specific basis [Arap et al. (1998) Science 279:377-380].
Interestingly, poor results have also been obtained when anti-angiogenic therapy (e.g., heparin, heparin-peptide treatment) directed at smooth muscle cell to proliferation has been practiced on myocardial ischemia in patients with coronary artery disease [Liu et al., Circulation, 79: 1374-1387 (1989); Goldman et al., Atherosclerosis, 65: 215-225 (1987); Wolinsky et al., JACC, 15 (2): 475-481 (1990)]. Various limitations associated with the use of such agents for the treatment of cardiovascular diseases included: (i) systemic toxicity creating intolerable level of risk for patients with cardiovascular diseases; (ii) interference with vascular wound healing following surgery; (iii) possible damage to surrounding endothelium and/or other medial smooth muscle cells.
In-light of these and the inherent obstacles associated with systemic administration of anti-angiogenic factors (i.e., manufacturing limitations based on in-vitro instability and high doses required; and peak kinetics of bolus administration attributing to sub-optimal effects) limit the effective use of angiogenic factors in treating neo-vascularization associated diseases.
With the identification of new genes that regulate the angiogenic process, somatic gene therapy has been attempted to overcome these limitations. Although, great efforts have been directed towards developing methods for gene therapy of cancer, cardiovascular and peripheral vascular diseases, there is still major obstacles to effective and specific gene delivery [for review see, Feldman A L. (2000) Cancer 89(6):1181-94] In general, the main limiting factor of gene therapy with a gene of interest, using a recombinant viral vector as a shuttle is the ability to specifically direct the gene of interest to the target tissue.
Attempts to overcome these limitations included the use of tissue-specific promoters conjugated to cytotoxic genes. For example, endothelial cell targeting of a cytotoxic gene, expressed under the control endothelial-specific promoters has been described by Jagger et al who used the KDR or E-selectin promoter to express TNFα specifically in endothelial cells [Jaggar R T. Et al. Hum Gene Ther (1997) 8(18):2239-47]. Ozaki et al used the von-Willebrand factor (vWF) promoter to deliver herpes simplex virus thymidine kinase (HSV-tk) to HUVEC [Hum Gene Ther (1996) 7(13):1483-90]. However, these promoters showed only weak activity and did not allow for high levels of expression.
An alternate approach presented by Kong and Crystal included a tumor specific expression of anti-angiogenic factors. To date, however, the toxicity of recombinant forms of endogenous anti-angiogenic agents has not been demonstrated although some synthetic anti-angiogenic agents have been associated with toxicity in preclinical models [Kong and Crystal (1998) J. Natl. Cancer Inst. 90:273-76].
Angiostatin has also been used as a possible anti-angiogenic agent (Falkman et al, Cell 1997 Jan. 24; 88(2):277-85), however due to the redundancy of factors involved in regulation of angiogenesis in tumors, it is highly unlikely that angiostatin therapy alone would be effective.
There is thus a widely recognized need for, and it would be highly advantageous to have a novel approach for efficiently down-regulating angiogenesis in specific tissue regions of a subject while being devoid of the toxic side effects characterizing prior art anti-angiogenesis approaches.